Electron microscopy of some rock phosphate dissolving bacteria and fungi

Bacteria Pseudomonas striata, Bacillus polymyxa, B. megaterium and B. pulvifaciens, and fungi Aspergillus awamori, A. niger and Penicillium digitatum dissolve tricalcium phosphate and, much less, Mussorie and Udaipur rock phosphate. The solubilizing power of fungi was higher than that of bacteria, the highest being with A. awamori and A. niger, and with P. striata. Electron microscopy of the various cultures showed an electron-dense layer on the bacterial surface after negative staining. The size of phosphate particles decreased by the microbial action, with tricalcium phosphate from 140--250 to 30--90 nm after three weeks of incubation.